This invention relates to fluidization, and more particularly to apparatus and process for carrying out fluidized bed operations.
Fluidized beds have been used for many years in the chemical industry for carrying out a wide variety of chemical reactions and/or unit operations. One of the primary advantages of fluidized bed systems arises from the fact that the high turbulence created in the bed provides high heat transfer characteristics as well as complete mixing of the solids and gases within the bed itself.
One of the primary disadvantages of fluidized bed systems is the phenomenon known as channeling whereby gas pockets are formed within the solids phase such that gases travel through the fluidized bed without intimately contacting the solid phase. That has been a particularly severe problem in the art in the fluidization of solid phases which have been recognized as difficult to fluidize, notably starch.
Significant improvements in the fluidization of solids which are difficult to fluidize have been achieved through the use of fluidization processes and apparatus as described in U.S. Pat. Nos. 3,967,975 and 4,021,927, the disclosures of which are incorporated herein by reference. The fluidized bed system utilized in those two patents comprises three distinct fluidized zones, an upper and lower fluidized zone, each of which is provided with paddle-type agitators to promote more complete mixing. Each of the upper and lower fluidized zones communicates each with the other by means of a plurality of tubular zones surrounded by heat transfer media whereby most, if not all, of the heat transfer to or from the fluidized bed is passed through the walls of the tubular fluidized zones.
The present invention is an improvement over the process and apparatus described in the foregoing patents, including improved means to discharge fluidized solids from the reactor and an improved process for use of the equipment in the drying of starch.